The taper bolts that secure the wings were found to be not in safety. This contravenes standard aviation practice. The locking feature of the fibre nuts into which the taper bolts were installed was found to be unserviceable in the left wing, and not used in the right wing. Given the total thickness of the spars and the length of the taper bolts, the bolts were long enough to engage the fibre nuts in a manner for safe installation. However, the right taper bolt did not penetrate the wing and fuselage spars far enough to engage the locknut safely. The taper bolts only pass through the top of the spar, and it is, therefore, not possible to visually inspect the inside of the spar with the wing installed. Although the taper bolts as found did not appear to be torqued, this could have been the result of the accident impact forces. Regardless, torquing the taper bolts ensures that they have engaged in the threads of the fibre locknut, but it does not ensure that they are in safety. Although the construction plans indicate a properly installed taper bolt will have a space of approximately 0.05inch between the head and the spar, this would be difficult to check with the aircraft fully assembled, and there is no means of verifying that the taper bolts are in safety once the wings are installed. The kit manufacturer was aware that it was possible to incorrectly install the flap during wing installation, and the manufacturer recommended guiding the pivot pin, on the inboard end of the flap drive torque tube, into the bronze bushing on the flap arm while installing the wing. The manufacturer also realized that an incorrectly installed flap could function normally on the ground, but under in-flight load conditions, the flap could retract, either partially or fully. As the uncommanded roll resulting from the flap asymmetry could not be corrected by opposite aileron input, the only means of correcting the uncommanded roll would be to retract the extended flap to remove the asymmetry. Reportedly, the pilot checked the flaps for correct installation and function before the accident flight. However, an examination of the aircraft indicated that the right flap was incorrectly installed, in that the torque tube pin was not secured in the flap arm bushing, which would allow the flap to retract in flight. It was determined that the flaps were up at the time of impact. Therefore, it is most likely that the pilot partially extended the flaps for the final slow-speed fly-past, and that the right flap retracted during the fly-past due to the improper installation. The pilot attempted to correct the problem with control stick input and by retracting the flaps. However, because of the altitude of the aircraft and the time required to retract the flaps, there was insufficient altitude to allow a successful recovery.Analysis The taper bolts that secure the wings were found to be not in safety. This contravenes standard aviation practice. The locking feature of the fibre nuts into which the taper bolts were installed was found to be unserviceable in the left wing, and not used in the right wing. Given the total thickness of the spars and the length of the taper bolts, the bolts were long enough to engage the fibre nuts in a manner for safe installation. However, the right taper bolt did not penetrate the wing and fuselage spars far enough to engage the locknut safely. The taper bolts only pass through the top of the spar, and it is, therefore, not possible to visually inspect the inside of the spar with the wing installed. Although the taper bolts as found did not appear to be torqued, this could have been the result of the accident impact forces. Regardless, torquing the taper bolts ensures that they have engaged in the threads of the fibre locknut, but it does not ensure that they are in safety. Although the construction plans indicate a properly installed taper bolt will have a space of approximately 0.05inch between the head and the spar, this would be difficult to check with the aircraft fully assembled, and there is no means of verifying that the taper bolts are in safety once the wings are installed. The kit manufacturer was aware that it was possible to incorrectly install the flap during wing installation, and the manufacturer recommended guiding the pivot pin, on the inboard end of the flap drive torque tube, into the bronze bushing on the flap arm while installing the wing. The manufacturer also realized that an incorrectly installed flap could function normally on the ground, but under in-flight load conditions, the flap could retract, either partially or fully. As the uncommanded roll resulting from the flap asymmetry could not be corrected by opposite aileron input, the only means of correcting the uncommanded roll would be to retract the extended flap to remove the asymmetry. Reportedly, the pilot checked the flaps for correct installation and function before the accident flight. However, an examination of the aircraft indicated that the right flap was incorrectly installed, in that the torque tube pin was not secured in the flap arm bushing, which would allow the flap to retract in flight. It was determined that the flaps were up at the time of impact. Therefore, it is most likely that the pilot partially extended the flaps for the final slow-speed fly-past, and that the right flap retracted during the fly-past due to the improper installation. The pilot attempted to correct the problem with control stick input and by retracting the flaps. However, because of the altitude of the aircraft and the time required to retract the flaps, there was insufficient altitude to allow a successful recovery. The right flap was incorrectly installed during the wing installation, which allowed the right flap to retract during the fly-past. This created a flap asymmetry that resulted in an uncommanded and uncontrollable right roll. The aircraft was at an altitude from which recovery was not possible before the aircraft struck the ground.Finding as to Causes and Contributing Factors The right flap was incorrectly installed during the wing installation, which allowed the right flap to retract during the fly-past. This created a flap asymmetry that resulted in an uncommanded and uncontrollable right roll. The aircraft was at an altitude from which recovery was not possible before the aircraft struck the ground. The right-wing taper bolt did not penetrate deep enough through the spars to engage the fibre locking feature of the locknut. Therefore, the taper bolt was not in safety at the time of the accident. The fibre locking feature of the left-wing locknut was worn and did not secure the left-wing taper bolt in safety.Findings as to Risk The right-wing taper bolt did not penetrate deep enough through the spars to engage the fibre locking feature of the locknut. Therefore, the taper bolt was not in safety at the time of the accident. The fibre locking feature of the left-wing locknut was worn and did not secure the left-wing taper bolt in safety.